The invention relates generally to motor vehicle tire pressure monitoring, and more particularly, to a housing assembly for a tire pressure sensor suitable for use in the direct monitoring of air pressure in tires.
Maintaining proper air pressure in tires is an important consideration for a motor vehicle operator. Both over-inflation and under-inflation of the vehicle's tires can have detrimental effects on vehicle handling, making the vehicle harder to control. Low tire pressure also causes the tire to run hotter thereby degrading the tire side wall and shortening the life of the tire. In addition, low tire pressure reduces fuel economy of the vehicle. With growing concerns over safety issues, vehicles today are being equipped with tire pressure monitoring systems that have been developed to alert the vehicle operator when the pressure in one or more of the vehicles tires is outside a recommended range.
Two general approaches have been favored for tire pressure-monitoring. One is an indirect method that involves the determination of the rolling radius of each wheel and tire assembly. The other is a direct method that employs a wireless transmission of a signal from a transducer module installed inside each tire.
The indirect or rolling radius method relies on signals generated by wheel rotation sensors, typically installed as part of an anti-lock braking system. The rolling radius represents the radius from the center of the tire to the generally flattened area referred to as the contact patch that engages the road surface. The rotational speed of each wheel can be accurately measured and the rolling radius of the wheel and tire assembly can be determined. This system of tire pressure monitoring (frequently referred to in the art as ABS-tire pressure monitoring) does not, however, provide absolute values of tire pressure. Rather, an inference of the tire pressure must be made based on the rolling radius.
Direct sensing systems monitor tire pressure directly from inside the tire. Wireless tire pressure sensors and radio frequency (RF) transmitters are mounted inside each tire. In each tire, the tire pressure sensed by the tire pressure sensor is transmitted by the transmitter to a receiver/controller located on the vehicle and is subsequently conveyed to the vehicle operator, usually in the form of a display. While the direct sensing systems have the potential to provide more accurate information, they also generally include batteries to power the sensors and transmitters. Battery life, the need to remove the tire for access to the batteries, and the need to rebalance the tires after battery replacement, together with the disposal of worn out batteries are the major shortcomings of direct sensing systems. The sensors and transmitters must also be able to withstand the harsh environment inside a vehicle tire that includes high temperatures, shock and vibration, and centrifugal forces from tire rotation.
A need exists for a protective mechanical package or housing to reliably and securely mount a direct tire pressure electronic sensing system in the harsh environment inside a vehicle tire.